The invention relates to a device for separating liquid from a gas-liquid mixture with a vortex tube through which the gas-liquid flows for generating centrifugal forces with acceleration &gt;50 g, the vortex tube having evacuation ports for discharge of the liquid to be separated, and a supply facility, particularly inlet nozzles, located in the inlet area of the vortex tube, with which the gas-liquid mixture is introduced into the the vortex tube and set in rotary motion in the tube. The vortex tube has a plurality of circular evacuation ports arranged one behind the other in the direction of flow and having a constant width over their length.
For separating liquids from gas-liquid mixtures, as for example natural gas, which mostly still contains certain portions of water, special separation devices are used which have a vortex tube. Such a vortex tube separator is described in German published patent applications DE-OS 2850020 and DE-OS 2850019 and consists of a double casing tube, inlet nozzles and regulating cone. The gas or gas mixture is introduced tangentially into the casing area through the inlet nozzles. In most cases, the gas already attains here the speed of sound, which depends upon the relationship between inlet and exit pressure. By precise layout and exact construction of the vortex tube, a vortex can be generated therein, in which centrifugal forces occur which are up to several million times greater than the acceleration due to gravity g (e.g., 50 to 5 million g). The maximum forces generated in a multiple cyclone separator with about fifty times the acceleration due to gravity are comparatively small.
On account of the Hilsch effect, a warm and a cold gas current are generated in the vortex tube. A regulating cone is situated at the end of the vortex tube, which permits separating the warm from the cold gas. These two gas currents can have temperature differences of up to 80.degree. K. To be sure, this is determined by the pressure ratio, the quantitative relationship between warm and cold gas, as well as by the gas composition.
During the almost isentropic expansion of the gas through the inlet nozzles, a condensation of components dissolved in the gas takes place. These are flung against the tube wall by the centrifugal forces occurring on account of the vortex. At the same time, the gas moves from the tube wall in the direction of the tube interior and thereby cools. By separating the liquid phase from the vortex tube, one obtains two circumscribed gas and liquid phases.
An interesting phenomenon of the vortex tube separator is that it can bring about a separation of heavy components from a gas stream despite a phase imbalance. This can be explained by the influence of the specific weight at high gravitational forces. After entering through the inlet nozzle, the liquid drops move together with the gas in a centrifugal field. This throws the liquid drops onto the tube wall. The liquid phase is separated before it can be heated up in the warm gas zone, or is separated in the cold gas stream. In this way, it is possible to obtain a separation of the condensate from the gas stream, although both phases are in imbalance. For drawing the liquid component off, one drainage opening is provided on each of the front and back ends of the vortex tube, through which the liquid-gas stream is pressed out on account of the high pressure. One of the drainage openings can be situated in the area of an immersion tube inserted into the interior of the vortex tube. In a separator connected to the drainage openings, the definitive separation of the liquid component from the gas part then takes place.
The path of the liquid drops depends upon their size. Larger liquid drops fly to the vortex tube wall in a short time and there likewise move axially in a spiral-shaped path. Depending upon the gas-liquid ratio and the physical properties of the liquid, the liquid current on the interior wall of the vortex tube is also changed. If, for example, little water is contained in an air-water mixture, the water does not form a film, and the drops basically move separately from one another. This is, for example, different with certain proportions of hydrocarbons and water, as for example with fuels, which form a fine film on the interior of the vortex tube wall.
The surface of the liquid film is not smooth on account of the adjacent gas current, so that due to the overlying wave structure, liquid drops can under certain conditions break away from this surface and get back into the gas-liquid mixture. It is necessary, therefore, among other things, also not to let the thickness of the liquid film being formed rise to such values that the surface of the liquid film becomes unstable and consequently leads to the separation of liquid drops.
From U.S. Pat. No. 3,884,660, a device is known in wherein the vortex tube consists of several tube segments between which ring-shaped evacuation ports are arranged. The gas-liquid mixture to be freed of the liquid is introduced through a supply facility into the inlet area of the vortex tube, which has guide vanes arranged at a predetermined angle, so that the gas-liquid mixture within the vortex tube executes a screw-shaped motion. On account of the centrifugal forces which arise (which, however, in contrast to the previously described vortex separators are much smaller) the liquid contained in the gas-liquid mixture precipitates on the interior wall of the tube segment and is guided out through the evacuation ports. The tube sections, which are fitted into one another and between which the evacuation ports are formed, can either have the same interior diameter, or each succeeding tube segment has a smaller interior diameter than the preceding tube segment. In both cases, the inserted end of the respective tube segment has a type of stripping edge in order to be able to undertake a separation of the liquid film from the gas-liquid mixture. Owing to the low centrifugal forces, the differential pressures between the inside and outside of the vortex tube are small (0.05-0.08 bar), so that the width of the evacuation ports which diminish toward the exterior, have to be selected very large. It has been shown that with wide evacuation ports, relatively high gas losses occur, and that narrowing the evacuation ports leads to a backup and to a negative influence on the laminar flow of the liquid film, so that only a part of the liquid film which has precipitated on the interior of the tube segment can actually be separated. The consequence of this is that the separated liquid drops enrich the gas-liquid mixture again. Since the evacuation ports form angles of &gt;20.degree. with the longitudinal axis of the vortex tube, a relatively abrupt deflection of the liquid film takes place, which likewise exerts a disadvantageous influence on the surface of the liquid film. It turns out that liquid drops separate from the surface upon abrupt deflections and return to the gas-liquid mixture.
The same also holds for the vortex tube known from UK Patent 1,146,262, whose evacuation ports to be sure have a constant width, whose axis however, likewise forms a large angle with the evacuation ports. In addition to this, the evacuation ports are short and empty into circular chambers for collecting the separated liquid.